%I #14 Jun 06 2020 03:35:17
%S 1,5,42,454,5680,78129
%N Number of alternating permutations on 2n letters that avoid a certain pattern of length 4 (see Lewis, 2012, Appendix, for precise definition).
%H J. B. Lewis, <a href="https://dspace.mit.edu/handle/1721.1/73444">Pattern Avoidance for Alternating Permutations and Reading Words of Tableaux</a>, Ph. D. Dissertation, Department of Mathematics, MIT, 2012. See Table A.2.
%Y Cf. A181197, A217799-A217830.
%K nonn,more
%O 1,2
%A _N. J. A. Sloane_, Oct 13 2012
%E Data corrected by _Andrew Howroyd_ after observation by _Gionata Neri_, May 02 2020